Reactive ink compositions and systems

ABSTRACT

Reactive ink compositions of the present invention utilize at least two reactive components, a base ink component and a curing component, that are applied to a receiving substrate separately. The base ink component includes an ink carrier, a compatible colorant, and a cross-linkable constituent, and the curing component is a cross-linking agent. Upon exposure of the base ink component to the curing component, at least a portion of the ink is cross-linked to provide a printed image that is durable and abrasion-resistant.

This application is a division of application Ser. No. 08/286,718, filedAug. 5, 1994, now U.S. Pat. No. 5,645,888, which is a division ofapplication Ser. No. 08/005,970 filed Jan. 19, 1993, now U.S. Pat. No.5,380,769.

TECHNICAL FIELD

The present invention relates generally to reactive ink compositionshaving at least two components that are applied separately to areceiving substrate. The present invention relates more specifically toreactive ink compositions including a base ink component that is printedon a receiving substrate using ink jet printing techniques to provide avisible image and a reactive curing component applied separately to thereceiving substrate or the printed image to produce a cross-linked inklayer.

BACKGROUND OF THE INVENTION

Ink jet printers operate by ejecting ink onto a receiving substrate incontrolled patterns of closely spaced ink droplets. By selectivelyregulating the pattern of ink droplets, ink jet printers can be used toproduce a wide variety of printed materials, including text, graphics,images, and the like. Moreover, ink jet printers are capable ofrecording permanent images on a wide variety of substrates, includinglight reflective substrates such as various types and grades of paper,and light transmissive substrates such as transparencies.

Ink jet printers designed for use with various types of inks are wellknown in the art. Solvent-based inks, including both aqueous andnon-aqueous, inks are well known. Images are formed by application ofsolvent-based inks to a receiving surface and subsequent removal, suchas by evaporation or diffusion, of the solvent. Although solvent-basedink printing systems are suitable for some applications, theirapplication is limited, primarily because the solvent tends to migrateinto porous surfaces, thereby reducing the resolution of the printedimage. Moreover, clogging of ink jet orifices as a result of solventevaporation is a serious problem in solvent-based ink jet systems.

Phase change inks are solid at ambient temperatures and liquid at theelevated operating temperatures of an ink jet printing device. Ink jetdroplets in the liquid phase are ejected from the printing device at anelevated operating temperature and rapidly solidify when they contactwith the surface of a substrate to form the predetermined pattern. Phasechange ink is advantageous for a variety of reasons. Problems associatedwith ink jet clogging resulting from solvent evaporation are largelyeliminated, thereby improving the reliability of ink jet printing.Because the ink droplets solidify rapidly upon contact with thesubstrate, migration of ink along the printing medium is substantiallyreduced, and image quality and resolution is therefore substantiallyimproved. Rapid solidification of phase change inks permits high qualityimages to be printed on a wide variety of porous and nonporous printingsubstrates.

Early references to phase change inks for ink jet printing involvedmonochrome inks jetted by electrostatic printing devices. Thus, forexample, U.S. Pat. No. 3,653,932 discloses a low melting point (30° C.to 50° C.) ink having a base comprising di-esters of sebacic acid. In asimilar process, U.S. Pat. No. 3,715,219 describes low melting point(30° C. to 60° C.) inks including a paraffin alcohol-based ink. Onedisadvantage of printing with low melting point phase change inks isthat they are susceptible to softening and tend to exhibit offsetproblems. Specifically, when substrates printed with low melting pointphase change inks are stacked or placed adjacent another surface, theink tends to adhere to adjacent surfaces, particularly if the printedsubstrates are exposed to high temperatures.

U.S. Pat. Nos. 4,390,369 and 4,484,948 describe methods for producingmonochrome phase change inks that employ a natural wax ink base, such asJapan wax, candelilla wax, and carnauba wax, which are printed using adrop-on-demand ink jet device at a temperature ranging between 65° C.and 75° C. U.S. Pat. No. 4,659,383 discloses a monochrome inkcomposition having an ink base including a C20-24 acid or alcohol, aketone, and an acrylic resin plasticizer. These monochrome inkcompositions are generally not durable and, when printed, become smudgedupon routine handling and folding. U.S. Pat. No. 4,684,956 disclosesphase change inks utilizing synthetic microcrystalline wax (hydrocarbonwax) and microcrystalline polyethylene wax. This molten composition canbe applied to a variety of porous and non-porous substrates usingdrop-on-demand ink jet application techniques.

Color phase change ink jet systems have also been developed. Color inkjet printers typically utilize three primary color inks, in addition toblack, that can provide a large spectrum of intermediate colors.Subtractive color mixing techniques utilizing cyan, magenta and yellowas primary colors are typically employed. European Patent ApplicationNos. 0187352 and 0206286 disclose phase change ink jet printing incolor. The base inks for these systems include fatty acids, athermoplastic polyethylene and a phase change material in the firstapplication; and the alcohol portion of a thermosetting resin pair, amixture of organic solvents (o- and p-toluene sulfonamide) and a dye inthe second application.

Although ink jet printing using phase change inks generally produceshigh quality printing on light reflective substrates, ink jet printingof colored inks onto light transmissive media for displaying colorimages by overhead projection has been problematic. Special coatings aregenerally provided on light transmissive media to absorb solvent whensolvent-based ink systems are used. See U.S. Pat. Nos. 4,503,111,4,547,405, and 4,555,437. The development of phase change inks that aresubstantially transparent provides improved capability to print imageson light transmissive substrates without requiring the use of specialcoatings. Phase change ink compositions disclosed in U.S. Pat. No.4,899,761 are exemplary. As a consequence of the three-dimensionalconfiguration of phase change ink droplets, however, phase change inkimages projected by overhead projection generally do not exhibit highcolor saturation and clarity and may require reorientation afterprinting.

PCT Patent Application No. WO 88/08788 is directed to a method oftreating transparencies printed with curved, light scattering inkdroplets to improve their projection qualities. The printed ink dropletsare overlaid with a transparent layer having an index of refraction thatis substantially the same as the index of refraction of the inkdroplets. Preferred coating materials include transparent polyurethaneand acrylic. In this manner, the refractive effect of the curvature ofthe ink droplets is reduced.

U.S. Pat. No. 4,992,304 discloses a system for printing phase change inkon light transmissive substrates such as transparencies wherein anadhesion promoter layer is interposed between the substrate and inklayer. Adhesion promoter layers comprise a thermoplastic material, suchas a thermoplastic polyamide.

In many ink jet printing systems, ink is printed directly onto thesurface of the final receiving substrate. An ink jet printing systemwherein an image is printed on an intermediate image transfer surfaceand subsequently transferred to the final receiving substrate isdisclosed in U.S. Pat. No. 4,538,156 to Durkee et al. Inks having apolyhydric alcohol base colored with dyes that do not wet the surface ofthe intermediate transfer drum are disclosed for use with the ink jetprinting system disclosed in the '156 patent.

U.S. Pat. Nos. 4,731,647 and 4,833,530 to Kohsahi disclose a systemwherein a solvent is deposited on colorant to dissolve the colorant andform a transferable ink drop. The colorants and solvent are depositeddirectly onto paper or plastic colorant transfer sheets to formtransferable ink droplets. The transferable drops are then contacttransferred to a final receiving substrate, such as paper.

U.S. Pat. No. 5,099,256 to Anderson describes an ink jet printing systemwherein ink is printed onto the surface of a thermally conductiveintermediate drum. The intermediate drum surface is coated with asuitable film-forming silicone polymer allegedly having a high surfaceenergy and high degree of surface roughness to prevent movement of theink droplets after they have been applied to the intermediate surface.The drum surface is heated to dehydrate the ink droplets prior totransfer to the recording medium.

U.S. Pat. No. 4,743,920 discloses a thermal transfer recording systemwherein ink forming a surface layer on an ink roll is selectively heatedor softened to transfer ink onto a recording medium. Supercoolable,heat-transferable inks having a heat-fusible binder are used in thissystem. The ink binders are obtained by mixing supercoolable substancessuch as plasticizers with conventional heat-fusible binders such asthermoplastic resins, amide resins, natural or synthetic waxes, or thelike.

U.S. Pat. No. 4,673,303 to Sansone et al. discloses an offset ink jetpostage printing method and apparatus in which an inking roll appliesink to the first region of a dye plate. A lubricating hydrophilic oil isapplied to the exterior surface of the printing drum or roll tofacilitate transfer of printed images from the intermediate drum ontothe receiving surface. The '303 patent also suggests that the ink can bemodified to increase its viscosity after it has been applied to thesurface of the drum upon exposure to electromagnetic radiation (visibleor UV) or heat, or upon addition of a catalyst.

U.S. Pat. No. 5,087,603 relates to self-cross-linking aqueous resindispersions obtained by emulsion-polymerizing a monomer composition inan aqueous medium. Cross-linking occurs upon evaporation of volatilecomponents to produce a film coating having improved adhesiveproperties, water and solvent resistance, and durability.

U.S. Pat. No. 4,421,816 discloses a dry transfer decal in which acarrier layer is formed by application of mutually cross-linkable liquidprepolymers to a base sheet. The carrier layer is cross-linked by theaction of heat or time, and ink layers are subsequently printed on thecarrier coat in the desired decal pattern. Upon application of the decalto a receiving surface, the carrier film is exposed and protects theunderlying ink layers from abrasion and degradation by exposure tosolvents and the like.

U.S. Pat. No. 4,454,179 discloses a dry transfer article in which theink component comprises a solvent-based ink, multi-component reactiveink, or actinic radiation curable ink. In multi-component reactivesystems, reactive components are dissolved or dispersed in a suitableliquid medium, printed, solvent evaporated and then cured by reaction ofthe reactive components. Multi-component reactive ink systems involvingcombination of a reactive polyol resin and polyisocyanate to producepolyurethane inks are disclosed. Moreover, the '179 patent disclosesthat actinic radiation curable ink systems entail use of reactiveprepolymers and monomers such as urethane acrylates responsive toactinic radiation (generally UV light) to effect curing.

Although many ink compositions and printing systems have been developedfor various applications for electronic computer driven printers, thedemand for increasingly higher resolution images and faster printingtimes, and the ability to print images on a variety of substrates,requires yet more refined ink compositions and ink jet printing systems.Specifically, there is a need for ink compositions and printing systemsthat can provide high resolution images on a variety of printingsubstrates at high printing rates. In addition to the foregoingrequirements, it is also important that the printed ink image isflexible, durable and non-abradable.

SUMMARY OF THE INVENTION

Reactive ink compositions of the present invention utilize at least tworeactive components, a base ink component and a curing component, thatare applied to a receiving substrate separately. The base ink componentis preferably applied to a receiving surface using ink jet printingtechniques and, upon exposure of the base ink component to the curingcomponent, a durable, cross-linked ink is produced.

The base ink component comprises a solvent-based (aqueous ornon-aqueous) or phase change ink carrier, a compatible colorant, and across-linkable constituent. Phase change ink carriers are generallypreferred for printing applications contemplated by the presentinvention because they produce high resolution images on a variety ofreceiving substrates. Solvent-based ink carriers having aqueous ornon-aqueous ink carriers are also described below and may be preferredfor certain applications. Colorants that are compatible with the inkcarrier are used to provide the subtractive primary colors. One or morecross-linkable constituents is also incorporated in the base inkcomponent. Under circumstances where the cross-linkable constituent andthe cross-linking agent are unreactive until a catalyst or other curingagent is introduced, both the cross-linkable constituent and across-linking agent may be incorporated in the ink carrier while thecatalyst serves as a curing component.

Curing components generally comprise a cross-linking agent or chainextender that is reactive with the cross-linkable constituent in thebase ink component to form a cross-linked ink. Cross-linking agents thatreversibly or irreversibly cross-link the ink composition may beemployed. A cross-linking catalyst may be provided in the base inkcomponent or the curing component, or it may be applied separately to asubstrate or printed ink layer to accelerate the cross-linking reaction.

The base ink component is preferably applied to a receiving substrateusing ink jet printing techniques. According to preferred embodiments,the base ink component is applied to an intermediate support surfaceusing ink jet printing techniques and subsequently transferred to thedesired receiving surface. The curing component may be applied to theintermediate support surface directly or in combination with an inkrelease agent. When the base ink component contacts the curing componentapplied to the intermediate transfer surface, a cross-linked inkinterface region is formed at the surface of the printed ink layeradjacent the intermediate transfer surface. Upon transfer of the printedimage from the intermediate support surface to the final receivingsubstrate, the cross-linked portion of the printed ink layer forms theouter, exposed layer of the printed substrate. An abrasion-resistantprinted ink layer having enhanced durability is thereby provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will becomeapparent upon consideration of the following detailed disclosure of theinvention, especially when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 illustrates a diagrammatic partially cross-sectional view of aprinting system having an intermediate support surface for receiving animage from an ink jet print head and means for applying a release filmlayer;

FIG. 2 illustrates an enlarged diagrammatic cross-sectional view of inkdroplets applied to an intermediate transfer surface, with cross-linkedportions of the ink droplets illustrated by cross-hatching; and

FIG. 3 illustrates an enlarged diagrammatic partially cross-sectionalview of cross-linked ink droplets after they have been contacttransferred from the intermediate support surface to a final receivingsubstrate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reactive ink systems of the present invention feature a curing componentcomprising a cross-linking agent and a base ink component comprising asolvent-based or phase change ink carrier, a compatible colorant, and across-linkable constituent. The base ink component and curing componentare applied to a receiving substrate separately and, upon contact withone another, produce a cross-linked printed product.

Base ink components suitable for use in the reactive ink compositionsand systems of the present invention are applied to a receiving surfaceusing any appropriate printing system, such as an ink jet or thermal waxprinting system. Base ink components suitable for ink jet printingtechniques must have certain physical and rheological properties.Specifically, ink jet printing techniques involve application of thebase ink component to a receiving surface in a relatively low viscosity,liquid form. Upon or shortly after printing, the low viscosity liquidbase ink dries and/or hardens to form a printed image that can behandled and manipulated. Thermal wax printing systems do not require inkto be jetted, but require transfer of ink in a liquid or semi-liquidform followed by rapid drying or hardening.

Ink jet printers and print heads suitable for use with the reactive inkcompositions and systems of the present invention are well known.Solvent-based inks, both aqueous and non-aqueous, can be printed usingboth thermal-type ink jet and piezoelectrically actuated printheadswhich eject ink droplets onto a receiving substrate. The Hewlett-PackardDesk Jet printer, for example, ejects ink by heating it to form abubble. Phase change inks are typically printed using a multi-orificedrop-on-demand ink jet printer that ejects ink droplets by compressing achamber with a piezoelectric transducer, such as occurs in the TektronixPhaser III printer.

Base ink components may be applied directly to the desired receivingsurface, or they may be printed on an intermediate support surface andsubsequently transferred to the final receiving substrate. The curingcomponent is applied to the desired or intermediate receiving surfaceseparately from the base ink component. For example, the curingcomponent may be applied to the desired receiving surface or to anintermediate support surface as a coating prior to printing with (ortransfer of) the base ink component. An exemplary imaging system usingan intermediate receiving surface is disclosed, for example, incopending U.S. Pat. No. 5,389,958 issued Feb. 14, 1995, and assigned tothe assignee of the present invention. Alternatively, the curingcomponent may be applied to a surface of the printed base ink componentafter printing or transfer from an intermediate to a desired receivingsurface.

FIG. 1 illustrates part of an exemplary printing system 10 adaptable foruse with reactive ink compositions of the present invention in which animage is printed on an intermediate support surface and then transferredfrom the intermediate surface to a final receiving substrate. Aprinthead 11 is supported by an appropriate housing and support elements(not shown) for ejecting ink in a liquid or molten state in rasterfashion onto an intermediate support surface 12 of rigid support 14.Printheads suitable for printing reactive ink base components of thepresent invention are known in the art, such as that disclosed in U.S.Pat. No. 5,087,930 issued Feb. 11, 1992 to Roy and assigned to theassignee of the present inventor.

Light reflective substrates such as various types and grades of paperand light transmissive substrates such as transparencies are appropriatesubstrates for use with reactive ink compositions and systems of thepresent invention. "Plain paper" is a preferred substrate, and papersuch as that supplied by Xerox Corporation and many other companies foruse in photocopy machines and laser printers is suitable. Many othercommonly available office papers are included in this category of plainpapers, including typewriter grade paper, standard bond papers, andletterhead paper. Xerox 4024 paper is a representative grade of plainpaper for the purposes of this invention.

Rigid support 14 preferably takes the form of a curved surface such as aroller surface, although it may be provided as a web, platen, or thelike. Rigid support 14 is constructed from relatively rigid materials,such as metallic aluminum-, nickel- or iron-containing materials;elastomeric materials such as fluoroelastomers, perfluoroelastomers,silicone rubber and polybutadiene; plastic materials such aspolytetrafluorethylene loaded with polyphenylene sulfide; thermoplasticssuch as polyethylene, nylon, and FEP; thermosets such as acetals; orceramics. Rigid support 14 may be formed from a laminar materialcomprising one or more of the compositions recited above, provided thatintermediate support surface 12 is sufficiently smooth and rigid todeform the ink droplets 26, best seen in FIGS. 2 and 3 applied tosupport surface 12 in a substantially uniform manner when the finalreceiving substrate 28 passes between rigid support 14 and a fixingsupport 22. Anodized aluminum is a preferred material for rigid support14.

The reactive base ink component of the present invention is applied tosupport surface 12 in the form of ink droplets 26. According topreferred embodiments, support surface 12 is coated with a chemicalcuring agent film 13 to facilitate cross-linking of cross-linkable inkdroplets 26. Chemical curing agent films 13 may be produced bydispersing or dissolving the appropriate chemical curing agent(described below) in a release fluid that facilitates transfer of inkdroplets 26 from support surface 12 to desired receiving surface 28.Even in reactive ink systems of the present invention wherein actinicradiation is employed as a curing agent or a chemical curing agent isapplied directly to a printed surface, support surface 12 is preferablycoated with a release film. Suitable release fluids for application tointermediate support surface 12 to facilitate transfer of ink dropletsinclude water, fluorinated oils, glycol, surfactants, mineral oil,silicone oil, functional oils or combinations thereof. Functional oilsmay comprise, for example, mercapto-silicone oils, fluorinated siliconeoils and the like.

Film applicator assembly 16 optionally comprises a reservoir and wickingpad 15 for applying film layer 13 to support surface 12. Suitableapplicator assemblies may also employ a web and web advancing mechanismto periodically present fresh web for contact with support surface 12.Wicking pad 15 preferably comprises any appropriate nonwoven synthetictextile having a relatively smooth surface. Polyester webs are suitable.In a preferred configuration, smooth wicking pad 15 is mounted atop aporous supporting material 18, such as a polyester felt. Both materialsare available from BMP Corporation as BMP products NR 90 and PE 1100-UL,respectively. Applicator apparatus 16 is mounted for retractablemovement upward into contact with and downwardly out of contact withsupport surface 12 by means of an appropriate mechanism, such as an aircylinder or an electrically actuated solenoid. Suitable apparatus forapplying a thin film to support surfaces are well known in the art.

The desired thickness of the film layer 13 on intermediate supportsurface 12 varies dependent upon the particular components in thecross-linking system and the printing system employed. The minimumthickness of the layer 13 is that required to achieve an effectivetransfer and can be as thin as about 0.05 microns. It is theorized thatthe layer 13 can be as thick as about 100 microns. The thickness of filmlayer 13 may generally be increased if textured support surfaces 12 areemployed.

Some appropriately small quantity of film layer 13 on intermediatesupport surface 12 also is transferred to final receiving substrate 28in areas adjacent transferred ink droplets 26. This transfer of the filmlayer is relatively nominal. More than one page of the final receivingsubstrate 28 may be processed before it is necessary to replenish thefilm layer on intermediate support surface 12.

FIG. 1 also illustrates a substrate guide 20 that facilitates passage ofthe final receiving substrate 28, such as paper, from a positive feeddevice (not shown) to a nip formed between the opposing arcuate surfacesof the fusing roller 23 and rigid support 14. Stripper fingers 25 (onlyone of which is shown) may also be pivotally mounted to printing system10 to facilitate removal of final receiving substrate 28 from theexposed surface of rigid support 14.

Fusing roller 23 preferably comprises a rigid metallic core constructed,for example, from steel overlaid with a resilient elastomeric layer 22.Suitable elastomeric materials include silicones, urethanes, nitriles,EPDM and other resilient materials having a durometer of from about 40to 45 Shore D. Elastomeric layer 22 engages the reverse (unprinted) sideof final receiving substrate 28, while the ink layer printed on supportsurface 12 (and/or curing agent/release film 13) is transferred to theadjacent surface of final receiving substrate 28. Ink droplets 26 arethereby transferred to the surface of final receiving substrate 28 andsimultaneously flattened and adhered to the surface of the receivingsubstrate. Using roller transfer systems, as illustrated, the printedink image is conveniently transferred from one surface to another byrotation of the rollers in opposite directions.

FIG. 2 diagrammatically illustrates the reaction of a cross-linkableconstituent in the base ink component forming droplets 26 with a curingcomponent comprising a cross-linking agent or chain extender provided infilm 13. The portions 29 of ink droplets 26 represent the cross-linkingreactions that take place at the interface between the base inkcomponent and an appropriate curing component. Similar cross-linkingreactions would take place upon exposure of the base ink component tocuring components using other techniques, such as exposure to actinicradiation or physical application of chemical cross-linking agents usingink jet printing techniques, or by spray, wiper or roller application,or the like. One of the benefits of the illustrated preferred embodimentis that the cross-linked portion of the ink droplets ultimately (i.e.after transfer to final receiving substrate 28) forms the exposedsurface of the desired substrate.

FIG. 3 diagrammatically illustrates the sequence involved whencross-linked ink droplets 26 are transferred from film layer 13 onintermediate support surface 12 to final receiving substrate 28. Asshown in FIG. 3, ink droplets 26 are transferred to final receivingsubstrate 28 with a small quantity of the film layer 13 attachedthereto. Also, as noted above, upon transfer of cross-linked inkdroplets to final receiving substrate 28, cross-linked portions 29,which are the most durable and abrasion resistant, are exposed to theenvironment.

Support surface 12 may optimally be heated by an appropriate heaterdevice 19. Heater 19 may be a radiant resistance heater positioned asshown or, more preferably, positioned internally within rigid support14. Heater devices 21 and 24 may also be employed in proximity to finalreceiving substrate guide 20 and/or in proximity to fusing roller 23,respectively. The desired temperature of the support surface 12 isdependent upon the composition of the film containing the cross-linkingagent, the phase change ink, and their reactivity.

Heater 21 preferably preheats final receiving substrate 28 prior tocontact transfer of ink droplets 26. It is theorized that heater 21raises the temperature of final receiving substrates comprising plainpaper to between about 50° C. and about 200° C. The thermal energy offinal receiving substrate 28 is kept sufficiently low so as to minimizeenergy consumption and optimize the completion of cross-linking on finalreceiving substrate 28. Heater 24, when employed, heats the fixingroller 23 to a temperature of between about 25° C. and about 200° C.Heater 24 may alternatively be provided internally within roller 23.

In operation, support surface 12 has a film layer comprising a liquidlayer containing an ink curing compound applied to its surface by theaction of the applicator assembly 16. Assembly 16 is positioned in araised application condition (as shown in FIG. 1) by an appropriatemechanism (not shown), such as an air cylinder, until the wicking pad 15is in contact with support surface 12. A uniformly thick film is therebydeposited on the support surface 12. Rigid support 14 rotates about ajournalled shaft in the direction shown by the arrow in FIG. 1, whilethe heater 19 heats the film layer and the surface of rigid support 14to the desired temperature. Once a film layer 13 has been applied tosupport surface 12, the applicator apparatus is lowered to a non-contactposition until application of another film layer is required.

Ink is applied to the exposed surface of film layer 13 by printhead 11.The ink is applied in molten state, with phase change ink having beenmelted from a solid state prior to printing by printhead 11. Phasechange ink droplets 26 may solidify or be kept in liquid form on thefilm layer 13 as rigid support 14 continues to rotate. Cross-linkingbegins at interface 29 and preferably takes place as the rigid support14 rotates and the ink droplets printed thereon approach the nip formedbetween rigid support 14 and fusing roller 23. Ultimately, ink droplets26 are contact transferred to final receiving substrate 28 as they aredeformed to their final image conformation and adhered to finalreceiving substrate 28. Ink droplets 26 are thus transferred and fixedto final receiving substrate 28 by application pressure and, optionally,heat. The image formed on final receiving substrate 28 by ink droplets26 cools to ambient temperature and, at ambient temperature, possessesimproved durability.

Reactive inks of the present invention may employ solvent-based (aqueousor non-aqueous) or phase change ink carriers. Phase change ink carriersare preferably in a solid form at ambient temperature and are convertedto a molten state by the application of heat. Precise temperaturerequirements vary, of course, according to the ink composition, buttypically range from about 85° C. to about 150° C. Maintaining the inkat temperatures above this range may cause degradation or chemicalbreakdown of the ink and is therefore undesirable. Suitable phase changeink carriers are described in copending U.S. Pat. No. 5,372,852 issuedDec. 13, 1994, and assigned to the assignee of the present invention.Additionally, U.S. Pat. No. 4,889,560 issued Dec. 26, 1989, assigned tothe assignee of the present invention, discloses useful ink carriers andis incorporated herein by reference in its entirety. The ink carriercomposition is combined with a compatible colorant, preferably acompatible subtractive primary colorant. The subtractive primarycolorants include four component dyes, namely, cyan, magenta, yellow andblack. Preferably, the subtractive primary colorants comprise dyes fromeither class of Color Index (C.I.) Solvent Dyes or Disperse Dyes asdescribed in The Color Index Revised Third Edition published by theSociety of Dyers and Colourists in conjunction with the AmericanAssociation of Textile Chemists and Colourists. Some C.I. Basic Dyeshave also been successful by generating, in essence, an in situ SolventDye by the addition of an equimolar amount of sodium stearate with theBasic Dye to the phase change ink carrier composition. Acid Dyes andDirect Dyes have also been found to be compatible to a certain extent.Suitable colorants are disclosed in U.S. Pat. No. 4,889,560, issued Dec.26, 1989, incorporated herein by reference.

In addition to the ink carrier and a compatible colorant, base inkcomponents of the present invention additionally comprise across-linkable constituent and/or chain extender. Upon exposure ofcross-linkable constituents in the reactive base ink components toselected cross-linking agents, the base ink component is cross-linked,at least in the area of exposure, to provide a cross-linked ink.

In general, one of three types of cross-linking systems may be used:irreversible chemical bond forming systems (covalent or non-covalent)using a chemical cross-linking agent; irreversible cross-linking systemsusing actinic radiation; or reversible cross-linking systems.Cross-linking catalysts may also be incorporated in one or bothcomponents of a reactive ink composition to accelerate cross-linking.The reactive ink compositions chosen for the particular reactive inkcross-linking system must, in addition to exhibiting desirablecross-linking characteristics, be compatible with the ink carrier andcolorant and exhibit desirable stability and viscosity properties.Additionally, cross-linkable constituents must be stable andnon-reactive with other base ink constituents such as plasticizers,tackifiers, viscosity modifiers, light stabilizers, anti-oxidants andthe like, at operating temperatures.

Corresponding curing components comprising cross-linking agents orpolymer chain extenders may be oil soluble, water soluble, organic,inorganic or metallic. Suitable curing components comprise across-linking agent or polymer chain extender and/or a cross-linkingcatalyst matched to the cross-linkable constituent contained in the baseink component.

Numerous cross-linking systems are known in the art and could be adaptedfor use in reactive ink compositions of the present invention. Exemplaryirreversible covalent cross-linking systems include: phenol-formaldehyderesins such as resoles and novolacs; unsaturated and alkyd polyesterscured through oxidative cross-linking mechanism; epoxy resins cured withamines, amine-terminated polyamides, amidoamides, acid catalysts,tertiary amine catalysts, carboxylic acids, anhydrides and phenols;isocyanates cured with active hydrogen functionalities such asmulti-functional hydroxyls or amines; vinyl esters cured with freeradical initiators; amino resins such as urea-formaldehyde ormelamine-formaldehyde cured with hydroxy functionalized resins in thepresence of an acid; acrylics cured with various functional groups,including hydroxyl, glycidyl, carboxylic, isocyanate, oxazolidine andazividine; silicones cured with free radical initiators; and unsaturatedhydrocarbons cured with sulfur or free radical initiators.

Exemplary non-covalent reversible cross-linking systems include:thermoplastic ionomers formed by curing an ethylene-acrylic acidcopolymer with a Group I or II metal salt; elastomeric ionomers formedby reacting carboxylated EPDM rubbers with zinc or calcium rosin salt;ionomers formed by reacting styrene carboxylic acid copolymers with aGroup I or II metal salt; polymers produced by dimerization of nitrosogroups with unsaturated polymers; and polymers produced by treatingcarboxyl-containing polymers with acetic anhydride to initiate anhydridecross-linking.

Cross-linking may also be achieved by exposing to various forms ofactinic radiation the cross-linkable constituent, which may be selectedfrom monomers, oligomers, polymers or copolymers of the acrylate family,such as urethane or epoxy acrylates available commercially from theSartomer Company of Exton, Pennsylvania or Polysciences, Inc. ofWarrenton, Pa. Any analagous compounds having acrylate functionalitycould also be employed. Some suitable forms of actinic radiationinclude, but are not limited to, cobalt 60; high and low energy electronaccelerators; light energy (both UV and visible); infrared energy;plasma or glow discharge; and lasers. The photoinitiator orcross-linking agent in such a system could be selected from suitablebenzophenones.

Ethylene-acrylic acid copolymers are a preferred cross-linkableconstituent for use with phase change carriers such as those describedin U.S. Patent No. 4,889,560, assigned to the assignee of the presentinvention and incorporated herein by reference. Ethylene-acrylic acidcopolymers having the following structures are especially preferred:##STR1## where x=from about 75% to about 99%; and y=from about 1% toabout 25%.

The molecular weight of preferred ethylene-acrylic acid copolymers isfrom about 500 grams per mole to about 10,000 grams per mole and n isdetermined by the molecular weight. Such ethylene-acrylic acidcopolymers are combined with the ink carrier and colorant composition inan amount from about 1 to about 30 weight percent.

Cross-linking agents suitable for cross-linking ethylene-acrylic acidcopolymers include amines such as diethylenetriamine,1,3-pentanediamine, 1,6-hexanediamine, polyoxypropylenediamine; andalcohols such as polyethylene glycol (PEG) and glycerol. Calcium acetatecan be used as a catalyst in these systems.

Multi-functional silane compounds are especially preferred curing agentsthat can be carried by silicone oils and are reactive withethylene-acrylic acid copolymers. Suitable "silane" compounds caninclude, but are not limited to, amines, alcohols, acids, expoxides orother appropriate functionalities dissolved or dispersed in siliconeoil. Exemplary suitable silane compounds includedimethyldiacetoxysilane, methyltriethoxysilane,vinylmethyldiacetoxysilane, methyltrimethoxysilane,ethyltriacetoxysilane, dimethyltetramethoxydisiloxane,methyltriacetoxysilane, tetraethoxysilane, vinyltriacetoxysilane,tetramethoxysilane, silicon tetraacetate, tetrapropoxysilane,dimethyldiethoxysilane, 1,1,3,3-tetramethyl-1,3-diethoxydisiloxane,bis(N-methylbenzylamido) ethoxymethylsilane, bis(dimethylamino)dimethylsilane, bis(dimethylamino) methylvinylsilane,tris(dimethylamino) methylsilane, tris(cyclohexylamino) methylsilane,vinyltris(methylethylketoximine)silane,methyltris(methylethylketoxime)silane, vinyl tris(isopropenoxy)silane,tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane,methylhydrocyclosiloxanes, 1,3-divinyltetramethyldisiloxane,1,3,5-trivinyl-1,1,3,5,5-pentamethyl trisiloxane, andtetravinyltetramethylcyclotetrasiloxane. Bis(dimethylamino)dimethylsilane and bis(dimethylamino) methylvinylsilane are preferred. Acompound sold by Dow-Corning as 2-6020 silane (N-(B-aminoethyl)γ-aminopropyltrimethoxysilane) is especially preferred as across-linking agent for ethylene-acrylic acid copolymer cross-linkableconstituents.

Although phase change reactive ink compositions are preferred for manyapplications, solvent (aqueous or non-aqueous) reactive ink compositionsmay be preferred for some applications. Aqueous inks are well known inthe art and are disclosed, for example, in U.S. Pat. Nos. 5,129,948 and5,017,644 assigned to Xerox Corporation and U.S. Pat. No. 5,108,505assigned to Hewlett-Packard-Company. A cross-linkable constituent suchas polyvinyl alcohol, polyacrylic acid, polyacrylamide,polyethyleneimine, polyvinylpyrrolidone, orpolyvinylpyrrolidone-co-acrylic acid copolymers could be incorporated inconventional aqueous solvent-based inks, for example, and cross-linkedusing a curing gent comprising a Group I or II metal ion such as sodiumtetraborate decahydrate or sodium hydroxide (NaOH), respectively,carried by an aqueous surfactant solution. Dispersing or dissolving thecuring agent in surfactant is desirable in many cases to wet anintermediate transfer surface.

Likewise, non-aqueous, oil-based reactive ink systems may also be used.Dimer acid, an oily bifunctional acid may, for example, be incorporatedin an oil-based ink carrier as a cross-linkable constituent. Rosin dineracid, a dimer of rosin abietic acid, may be a preferred cross-linkableconstituent in oil-based inks. The curing component for this type ofcross-linkable oil-based ink may comprise multi-functional alcohols,such as glycerol or polyvinyl alcohol, or polyamines dispersed ordissolved in non-aqueous surfactant solutions. Pentaerythritol may alsobe used as a curing component for an oil-based ink comprising dimeracid, and maleic anhydride may be employed as a catalyst. Anotheroil-based ink system may include a glycol constituent that iscross-linkable upon exposure to an isocyanate curing agent.

Several experiments were conducted to test the feasibility of reactiveink compositions and systems. The following examples are presented toillustrate the types of materials that can be successfully employedwithout limiting the invention to specific materials, structures orsystems employed.

EXAMPLE I

Ethylene-acrylic acid (EAA) copolymer AC-5180 (available from AlliedSignal) was mixed at about 50% by weight in a small aluminum pan withabout 50% by weight ink carrier with colorant and heated to about 125°C. The colorant was about 1.9% by weight yellow dye SY 146 Orasol Yellow4GN (C.I. Solvent Yellow 146 available from Ciba Geigy. The remainder ofthe ink carrier consisted of:

    ______________________________________    about 42.0%            S-180 monoamide  (Witco Chemical Co.)    about 21.5%            Unirez 2970 tetramide                             (Union Camp)    about 27.0%            KE-311 Kemamide tackifier                             (Witco Chemical Co.)    about 9.5%            Santiciser 278 plasticizer                             (Monsanto Chemical Co.)    ______________________________________

The colored ink base component was kept over a hot plate and stirredmanually for about 5 minutes or until the mixture became homogeneous. Anexcess amount of about 10% by weight diethylenetriamine (DETA) curingagent from a two-part epoxy resin sold by the Dexter Corporation underthe tradename Epoxi-Patch was stirred into ink base mixture for about 1minute over a hot plate until it formed a gel. The resultant mixture wasspread in a thin film onto a piece of paper and was allowed to cool toambient temperature.

The resulting yellow film was extremely hard, abrasion-resistant, toughand flexible upon folding of the paper. In contrast, a Phaser IIIColorStix™ solid ink stick sold by Tektronix, Inc. produces a less hard,tough and abrasion-resistant film upon jetting from an ink jet printeronto paper substrate. However, the colored ink mixture with EAA was tooviscous to jet from an ink jet device. To permit application of thecolored base ink component using ink jet printing techniques, theviscosity of the base ink component must be reduced. This could beaccomplished by reducing the EAA, tetramide and tackifier weightpercentages, by reducing the molecular weight of the EAA, or both.

EXAMPLE II

A base ink component was made using the same procedure and weightpercentages for the ink carrier and colorant composition as in ExampleI, except that the DETA curing agent was replaced with a mixture of thefollowing constituents in the weight percentages shown below:

about 60.0% Glycerol

about 2.0% Calcium acetate

A dye having the same composition but substituting magenta for yellowcolorant was also made.

The resulting dyes were applied to paper in a film as described above.Both the yellow and magenta inks were less abrasion-resistant than thefilm formed in Example I, although still tougher and more durable thanthe film formed by the ColorStix™ solid ink sticks upon jetting. Thebase ink components were still too viscous to be applied using ink jetprinting techniques, and similar adjustments to the colored base inkcomponents as suggested in Example I would be necessary to provide inksthat could be applied using ink jet printing techniques.

EXAMPLE III

An ink composition according to the present invention was prepared asfollows: about 177.27 grams of stearyl stearamide, about 17.75 grams ofalkylbenzyl phthalate and about 40.10 grams of ethylene-acrylic acidcopolymer were mixed in a 500 ml. beaker and heated with stirring to atemperature of 120° C. After a homogeneous solution of the materials wasachieved, the molten phase change ink composition was filtered through aheated Mott apparatus using Whatman #3 filter paper and a pressure of 15psi. The molten phase change ink was placed in a beaker at 105° C. About1.91 grams of Orasol Yellow 4GN (C.I. Solvent Yellow 146) colorant fromCiba Geigy was added to the mixture, which was then stirred at about105° C. for about 1 hour. The resulting ink composition was filtered inthe heated Mott apparatus at about 100° C. The filtrate was poured intoa mold, filtered through Whatman #3 filter paper and allowed to solidifyto form solid ink sticks. The viscosity of the formulation was about 14centipoises at about 140 degrees centigrade. This formulation issuitable for jetting from an ink jet device.

A dispersion of about 50% by weight ofN-(-aminoethyl)--aminopropyltrimethoxysilane, available under the tradename Dow Corning Z-6020 silane, and about 50% by weight of silicone oilavailable under the trade name Dow Corning 200 was mixed together atroom temperature.

The cross-linking reaction was conducted as follows: a test fixturehaving a rotatably mounted anodized aluminum drum and a diameter ofabout 4.13 inches was positioned adjacent and in close proximity to atransfer and fusing roller of smaller diameter. A piezoelectricallydriven printhead loaded with phase change ink was positionedintermediate the drum and the transfer and fusing roller to deliver theprimary colors of cyan, magenta, yellow and black to the exposed surfaceof a thin liquid layer of an intermediate support surface in rasterfashion. The drum surface was coated with a liquid layer consisting ofthe dispersion of Dow Corning Z-6020 silane and Dow Corning 200 siliconeoil described above. The dispersion was applied with a wick/feltlaminate applicator having a steel backing plate. The drum temperaturewas maintained at about 65° C. Paper was used as the final receivingsubstrate and was preheated by an external heating device with asetpoint temperature setting of about 120° C. prior to being broughtinto contact with the transferred ink image. During imaging, the drumwas rotated at a surface speed of about 33.3 inches per second. Duringtransfer and fixing, the surface speed of the roller was about 5 inchesper second. A full color solid yellow test image was imaged by theprinthead on the liquid intermediate transfer layer and transferred toXerox 4024 plain copy paper. The transferred image was of good quality.

The uniformity of the cross-linking reactions between the acrylic acidgroups in the phase change ink composition and the functional silanes inthe intermediate transfer layer was determined by the color shift of theprinted image from a bright, vibrant yellow in the uncross-linked imageto a reddish yellow in the cross-linked image. The color shift seem tobe uniform across the page of the printed image. The ink was determinedto be cross-linked because it remained insoluble in hot toluene.Cross-linked materials cannot be dissolved in any solvent, whileuncross-linked phase change ink is very soluble in hot toluene.

EXAMPLE IV

An ink according to the present invention can be prepared as follows:Mix about 42.0% S-180 monoamide (Witco Chemical Co.); about 21.5% Unirez2970 tetramide (Union Camp); about 9.5% Santiciser 278 plasticizer(Monsanto Chemical Co.); about 1.9% yellow dye Orasol Yellow 4GN (C.I.Solvent Yellow 146) (Ciba Geigy); and about 25.1% rosin diner acid. Heatthe mixture to a temperature of about 125° and stir until a homogeneoussolution is achieved.

An excess amount of about 10% by weight diethylenetriamine (DETA) curingagent, from a two-part epoxy resin sold under the tradename Epoxi-Patchby the Dexter Corporation can be stirred into ink base mixture for about1 minute over a hot plate until it forms a gel. The resultant mixturecan be spread in a thin film onto a piece of paper and allowed to coolto ambient temperature. The resulting film would be tough,abrasion-resistant and durable, but the ink would be too viscous toapply using ink jet printing techniques.

While the invention has been described above with reference to thespecific embodiments thereof, it will be apparent to skilled personsthat many changes, modifications and variations may be made to thedetails of the invention described herein without departing from theunderlying principles of the inventive concept disclosed. For example,it should be noted that the curing process employed with reactive inksystems of the present invention can be either a single step or amulti-step process. In a single step process the curing would occurduring the transfer and fixing step of transferring the printed imagefrom the intermediate transfer surface to the final receiving surface orsubstrate. In a multi-step process, the curing would occur at separatelocations and at separate times, such as during the transfer and fixingstep and during a subsequent post-processing step.

Also, it is possible that aqueous based inks could be employed whereinitially a gel is formed, such as by the reaction of a component in theink, for example polyvinylpyrrolidone, and a component of the liquidlayer to which the ink is applied, such as polyacrylic acid. Oncesufficient heat of reaction is supplied, the cross-linking agent in theink, such as polyethyleneimine, will cross-link with the carboxylic acidfunctionality of polyacrylic acid. The ink composition, in addition towater, can also include an appropriate biocide, glycerol, and a suitablecoloring agent, such as a dye. The liquid layer can include asurfactant, in addition to water and the polyacrylic acid.

Accordingly, the spirit and broad scope of the appended claims isintended to embrace all such changes, modifications and variations thatmay occur to one of ordinary skill in the art upon a reading of thedisclosure.

We claim:
 1. A reactive ink system for use in ink jet printerscomprising:a base ink component having an ink carrier, a compatiblecolorant, and a cross-linkable constituent; and a cross-linking agentreactive with the cross-linkable constituent in the base ink component;and a substrate support surface; means for applying cross-linking agenton the substrate support surface; means for applying a predeterminedpattern of the base ink component on the substrate support surface afterthe cross-linking agent has been applied on the substrate supportsurface to create a cross-linked ink pattern, and means for placing asubstrate in contact with the substrate support surface to transfer thecross-linked ink pattern to the substrate from the substrate supportsurface.
 2. A reactive ink system according to claim 1, wherein the inkcarrier is a phase change ink carrier.
 3. A reactive ink systemaccording to claim 1, wherein the ink carrier is a solvent based inkcarrier.
 4. A reactive ink system according to claim 3, wherein the inkcarrier is aqueous and the cross-linkable constituent is one selectedfrom the group consisting of polyvinyl alcohol, polyacrylic acid,polyacrylamide, polyethyleneimine, polyvinylpyrrolidone andpolyvinylpyrrolidone-co-acrylic acid.
 5. A reactive ink system accordingto claim 4, wherein the cross-linkable constituent is anethylene-acrylic acid copolymer having the following structure: ##STR2##where x=from about 75% to about 99%; and y=from about 1% to about 25%.6. A reactive ink system according to claim 4, wherein the cross-linkingagent comprises a Group I or II metal ion.
 7. A reactive ink systemaccording to claim 6, wherein the cross-linking agent comprises sodiumtetraborate decahydrate or sodium hydroxide.
 8. A reactive ink systemaccording to claim 3, wherein the ink carrier is non-aqueous and thecross-linkable constituent is a dimer acid.
 9. A reactive ink systemaccording to claim 8, wherein the cross-linkable constituent is rosindimer acid.
 10. A reactive ink according to claim 8, wherein thecross-linking agent is a multi-functional alcohol or polyamine.
 11. Areactive ink system according to claim 1, wherein the cross-linkableconstituent is one selected from the group consisting of monomers,oligomers, polymers or copolymers of urethane or epoxy acrylates.
 12. Areactive ink system according to claim 11 wherein the cross-linkableconstituent is cross linked upon exposure to radiation.
 13. A reactiveink system according to claim 12 wherein the radiation is one selectedfrom the group consisting of: cobalt 60; high and low energy electronaccelerators; visible light; UV light; infrared energy; plasmadischarge; glow discharge; and lasers.
 14. A reactive ink systemaccording to claim 1, wherein the cross-linkable constituent is anethylene-acrylic acid copolymer having the following structure: ##STR3##where x=from about 75% to about 99%; and y=from about 1% to about 25%.15. A reactive ink system according to claim 14, comprising theethylene-acrylic copolymer having a molecular weight of about 500 toabout 10,000 grams/mole.
 16. A reactive ink system according to claim14, wherein the cross-linkable constituent comprises from about 1 toabout 30 weight percent of the base ink component.
 17. A reactive inksystem according to claim wherein the cross-linking agent is selectedfrom the group consisting of diethylene triamine; 1,3-pentanediamine;1,6-hexandiamine; polyoxypropylenediamine; polyethylene glycol; andglycerol.
 18. A reactive ink system according to claim 14, wherein thecross-linking agent is a functional silane compound.
 19. A reactive inksystem according to claim 8, wherein the cross-linking agent is selectedfrom the group consisting of: dimethyldiacetoxysilane,methyltriethoxysilane, vinylmethyldiacetoxysilane,methyltrimethoxysilane, ethyltriacetoxysilane,dimethyltetramethoxydisiloxane, methyltriacetoxysilane,tetraethoxysilane, vinyltriacetoxysilane, tetramethoxysilane, silicontetraacetate, tetrapropoxysilane, dimethyldiethoxysilane,1,1,3,3-tetramethyl-1,3-diethoxydisiloxane, bis(N-methylbenzylamido)ethoxymethylsilane, bis(dimethylamino) dimethylsilane,bis(dimethylamino) methylvinylsilane, tris(dimethylamino) methylsilane,tris(cyclohexylamino) methylsilane,vinyltris(methylethylketoximine)silane,methyltris(methylethylketoxime)silane, vinyl tris(isopropenoxy)silane,tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane,methylhydrocyclosiloxanes, 1,3-divinyltetramethyldisiloxane,1,3,5-trivinyl-1,1,3,5,5-pentamethyl trisiloxane, andtetravinyltetramethylcyclotetrasiloxane.
 20. A reactive ink systemaccording to claim 1, additionally comprising a catalyst component. 21.A reactive ink system according to claim 1, additionally comprising acatalyst component.